Jump-Over Cables Improve Signal Integrity

Cables that bypass PCB traces are making headway into high-speed digital designs because they lose less signal.

With 56-Gbit/s links coming online inside datacenter switches, PCB traces are showing signs of stress. Getting signals across a board from an I/O connector at a board's edge to an FPGA or ASIC is harder than ever. Signal losses mount.

To mitigate the losses, connector companies have developed what I call "jump-over" cable assemblies that bypass PCB traces. These cables, with trade names that include BiPass (Molex), Sliver (TE Connectivity), and Firefly (Samtec), are becoming popular with designers.

The market for these cable assemblies, which also connect boards to backplanes and between backplanes, seems on the cusp of significant growth as 56-Gbit/s PAM4 signals come into use in switches and routers. While numbers aren't yet available, connector makers report rising sales. When asked by EE Times, Bishop & Associates, which traces the connector and cable markets, doesn't have numbers for this market segment, at least not yet.

While these jump-over cable assemblies can improve signal integrity and minimize bit errors, they could be just a temporary solution to the problem. Optical waveguides on PCBs could render these cables obsolete. But optical waveguides, like silicon photonics, seem to always be five years away. We've been hearing about these technologies for more than 10 years. EE Times reported earlier this year that silicon photonics is merging ahead. I'll believe it when I see it. In the meantime, jump-over cable assemblies will continue to take hold.